Semiconductor device

ABSTRACT

A semiconductor device is equipped with fuses each made of a conductive material vertically extended through an insulator layer employed in the semiconductor device. Holes are formed which vertically penetrate the insulator layer. Sidewalls are formed on their corresponding wall surfaces of the holes. The holes formed with the sidewalls are buried with a conductive material.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device-equipped withfuses and a method of manufacturing the same.

2. Description of the Related Art

In a semiconductor device, a fuse is used to relieve a defect byredundancy substitution in a memory and control or adjust a resistancevalue employed in a resistance circuit, i.e., trim the resistance value.One example of a conventional fuse is shown in Japanese laid-open PatentNo. 2000-243213.

The present fuse is vertically disposed on the surface of a substrate.The fuse penetrates an insulator layer and is connected to a conductivepath on the surface of the substrate. The fuse has an advantage that thearea occupied by the fuse on a semiconductor chip becomes small owing tothe vertical provision of the fuse in this way.

The fuse is blown by Joule heat of a current that flows through the fuseitself. The Joule heat rises as the cross-sectional area thereof becomessmall, and the fuse is apt to melt down. The more the fuse is reduced insize, the more the semiconductor device can be scaled down. This isbecause the size of a portion which is connected to the fuse and causesa fuse blowing current to flow therethrough can be reduced in accordancewith the fuse as well as the ability to reduce the size of the fuse.

With the scaling up of an integrated circuit constituting asemiconductor device in particular, the number of fuses mounted on onechip tends to increase. The influence of the sizes of individual fuseson the overall size of the chip is becoming increasingly significant.

Therefore, the conventional fuse has a problem in that itscross-sectional area could be merely reduced to the minimum size definedby a micro-fabrication technique.

SUMMARY OF THE INVENTION

The present invention aims to make it possible to reduce across-sectional area of a fuse and thereby to reduce a cross-section ofa wiring connected to the fuse.

According to one aspect of the present invention, there is provided asemiconductor device comprising:

-   -   a substrate;    -   a first insulator layer formed on the substrate;    -   a first conductive layer formed on the first insulator layer;    -   a second insulator layer formed on the first conductive layer;    -   a second conductive layer formed on the second insulator layer;    -   sidewalls each formed on a side face of a hole vertically        extended through the second insulator layer; and    -   fuses each formed of a conductive material that buries a space        defined inside the sidewall, the fuse having a lower end        connected to the first conductive layer and an upper end        connected to the second conductive layer.

According to another aspect of the present invention, there is provideda method of manufacturing a semiconductor device equipped with fuseseach composed of a conductive material that vertically penetrates aninsulator layer, comprising the following steps of:

-   -   forming holes each vertically extended through the insulator        layer;    -   forming sidewalls on wall surfaces of the holes respectively;        and    -   forming fuses by burying the holes formed with the sidewalls        with the conductive material.

According to the present invention, sidewalls are respectively formedinside through holes defined in an insulator layer, and fuses are formedby burying only their inner sides with a conductor. Therefore, thesectional area of the fuse can be set smaller than that of the throughhole. It is thus possible to fabricate a fuse having a sectional arealess than or equal to a dimensional limitation under a micro-fabricationtechnique at the formation of the through hole. Accordingly, across-section and a line width of a portion connected to the fuse tocause a fusing current to flow therethrough can be reduced as well asthe fuse. By extension, the overall size of a semiconductor device canbe reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming the subject matter which is regarded as theinvention, it is believed that the invention, the objects and featuresof the invention and further objects, features and advantages thereofwill be better understood from the following description taken inconnection with the accompanying drawings in which:

FIG. 1 is a cross-sectional view showing a semiconductor device formedby a manufacturing method thereof according to one embodiment of thepresent invention;

FIG. 2 is a cross-sectional view illustrating a state in which a secondinsulator layer is formed in the manufacturing method according to theone embodiment of the present invention;

FIG. 3 is a cross-sectional view depicting a state in which a resistpattern is formed in the manufacturing method according to the oneembodiment of the present invention;

FIG. 4 is a cross-sectional view showing a state in which through holesare defined in the second insulator layer in the manufacturing methodaccording to the one embodiment of the present invention;

FIG. 5 is a cross-sectional view illustrating a state in which firstlayers corresponding to sidewalls are formed in the through holesrespectively in the manufacturing method according to the one embodimentof the present invention;

FIG. 6 is a cross-sectional view showing a state in which second layerscorresponding to sidewalls are formed in the through holes in themanufacturing method according to the one embodiment of the presentinvention;

FIG. 7 is a cross-sectional view depicting a state in which spacesdefined inside the sidewalls of the through holes are buried withconductors in the manufacturing method according to the one embodimentof the present invention;

FIG. 8 is a cross-sectional view showing a state in which a secondconductive layer is formed in the manufacturing method according to theone embodiment of the present invention; and

FIG. 9 is a cross-sectional view depicting an example illustrative ofsidewalls different from above.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will hereinafter bedescribed with reference to the accompanying drawings.

FIG. 1 shows a semiconductor device 10 according to one embodiment ofthe present invention. The semiconductor device 10 includes asemiconductor substrate 12, a first insulator layer 14 formed on thesemiconductor substrate 12, a first conductive layer 16 formed on thefirst insulator layer 14, a second insulator layer 18 formed on thefirst conductive layer 16, a second conductive layer 20 formed on thesecond insulator layer 18 and a third insulator layer 22 formed on thesecond conductive layer 20.

The semiconductor substrate 12 is a silicon substrate. The firstinsulator layer 14 is formed of silicon oxide.

The first conductive layer 16 is formed of a metal such as aluminum. Thefirst conductive layer 16 serves as interconnections. The secondinsulator layer 18 is formed of silicon oxide.

The second conductive layer 20 is formed of a metal such as aluminum.The second conductive layer 20 serves as interconnections. The thirdinsulator layer 22 is formed of silicon oxide.

The second insulator layer 18 is formed with through holes 24 thatpenetrate the insulator layer 18 vertically, i.e., in the directionnormal to the surface of the semiconductor substrate 12. Sidewalls 26are formed on their corresponding wall surfaces of the through holes 24.

Each of the sidewalls 26 comprises a first layer 28 formed on the wallsurface of the through hole 24 and a second layer 30 formed on the firstlayer 28 (inside the first layer 28).

The first layer 28 is composed of silicon nitride and the second layer30 is made of silicon oxide.

A conductor 32 is formed so as to bury a space defined inside eachsidewall 26. The conductor 32 constitutes a fuse and connects the firstinsulator layer 14 and the second insulator layer 18 to each other.

A method of manufacturing a semiconductor device including the fuse 32will be explained below.

As shown in FIG. 2, a first insulator layer 14 is first formed on asubstrate 12. Next, a first conductive layer 16 is formed thereon. T hefirst conductive layer 16 can be formed by forming a metal layer overthe entire surface and patterning it. Next, a second insulator layer 18is formed.

Next, as shown in FIG. 4, through holes 24 are defined in the secondinsulator layer 18. The through holes 24 are respectively circular insection.

The formation of the through holes 24 is performed by photolithography.That is, as shown in FIG. 3 by way of example, a resist film 34 isformed over the whole surface of the first conductive layer 16 andselectively exposed, followed by patterning of the resist film 34,whereby a resist pattern 34 having through holes 36 in formingpredeterminate regions of the through holes 24 (see FIG. 4) is obtained.The through holes 24 are formed by etching the first conductive layer 16with the resist pattern 24 as a mask. The size of each through hole 36defined in the resist pattern 34 is subjected to constraints byresolution of selective exposure.

Next, as shown in FIG. 5, the resist pattern 34 is removed and a firstlayer 28 of a sidewall 26 is formed in each through hole 24. Forinstance, a film of silicon nitride used as a material for the firstlayer 28 of the sidewall 26 is formed over the entire surface of thesubstrate by LP-CVD (Low-Pressure CVD) with SiH₂Cl₂ and NH₄ as gases andthereafter anisotropically etched to form the corresponding first layer28.

Next, as shown in FIG. 6, a second layer 30 is formed inside the firstlayer 28 of the sidewall 26 of each through hole 24. For instance, afilm of silicon oxide used as a material for the second layer 30 isformed over the whole surface of the substrate by LP-CVD with SiH₄ andN₂O as gases and thereafter anisotropically etched to form thecorresponding second layer 30.

The first layer 28 and the second layer 30 are formed as described aboveso that each sidewall 26 is formed. A space 38 extending in the verticaldirection is formed inside each sidewall 26.

The first layer 28 and the second layer 30 are both minimized inthickness at a top-end portion (corresponding to a portion farthermostfrom the substrate 12) of each through hole 24 and gradually increase inthickness as they come to the lower side (they approach the substrate12). Thus, the overall thickness of the sidewall 26 is smallest at thetop-end portion of the through hole 24 and becomes gradually large as itcomes to the lower side.

The space 38 has a transverse section substantially circular in a mannersimilar to the through hole 24 and is smaller in transversecross-sectional area than the through hole 24. The transverse sectionalarea of the space 38 is largest at the top-end portion of the throughhole 24 with a change in the thickness of the sidewall 26 and becomesgradually small as it reaches the lower side.

Next, as shown in FIG. 7, the space formed inside each sidewall 26 isburied with a conductor material such as aluminum to thereby form aconductor 28 which serves as a fuse. The conductor 28 is connected tothe first conductive layer 16 at its lower end.

Next, as shown in FIG. 8, a second conductive layer 20 is formed. Thesecond conductive layer 20 is connected to the conductor 28 at its lowersurface.

Next, as shown in FIG. 1, a third insulator layer 22 is formed.

The shape of the conductor 28 used as a fuse is identical to that of thespace 38, and its transverse cross-sectional area is smaller than thatof the through hole 24. It is thus possible to obtain a fuse having across-sectional area smaller than the minimum dimension of the throughhole 24 subjected to limitations due to the resolution of exposure andthe like.

When the sidewall 26 is formed by the two layers and the first layer 28brought into contact with the side face of each through hole 24 isformed of the silicon nitride film as in the example described above,the component of the conductor such as aluminum is dispersed when theconductor has molten down by fusion. It is however possible to stop suchdispersion by virtue of the silicon nitride film.

Incidentally, when the conductive material formed as the fuse 32 and thematerial of the second conductive layer 20 are identical in the aboveembodiment, the process of burying the conductor material formed as thefuse 32 in the space lying in each through hole 24 and the process offorming the second conductive layer 20 can be treated as one continuousprocess.

On the other hand, when the conductor material formed as the fuse 32 andthe material of the second conductive layer 20 are different from eachother, the process of embedding the conductor material formed as thefuse 32 into the space formed inside each through hole 24 is executedand thereafter the surface thereof is planarized by CMP (ChemicalMechanical Polishing) or the like. Further, the excess fuse materialthat overflows from or extends off the space 38 is removed, followed byformation of the second conductive layer 20.

In the aforementioned embodiment, the sidewall 26 is thinnest at thetop-end portion of each through hole 24 and becomes gradually thick asit approaches the lower side. With it change, the space 38 formed insidethe sidewall 26, accordingly, the transverse sectional area of the fuse32 formed by burying it is largest at the top-end portion and becomessmall as it approaches the lower side. However, as shown in FIG. 9 inreverse, a sidewall 26 thin on its lower side and thick on its upperside is formed and then a fuse 32 having a transverse section large onits lower side and small on its upper side may be formed. A sidewall 26which is thinnest at its lower end (corresponding to a portion closestto a substrate 12) and becomes thick as it approaches its upper side, isformed and then a fuse 32 having a transverse section which is largestat its lower end and becomes small as it approaches its upper side, maybe formed. If done in this way, then the blowing of a fuse becomeseasier.

A film of silicon oxide that constitutes a second layer 30 of thesidewall 26 shown in FIG. 9 can be formed by AP-CVD (AtmosphericPressure CVD) with SiH₄ and O₂ as gases.

Incidentally, although the conductor that constitutes the fuse 32 hasbeen formed of aluminum in the above embodiment, an alloy composedprincipally of aluminum may be used. Alternatively, copper (Cu),titanium (Ti), tungsten (W) or an alloy with these as principalcomponents may be adopted.

While the present invention has been described with reference to theillustrative embodiments, this description is not intended to beconstrued in a limiting sense. Various modifications of the illustrativeembodiments, as well as other embodiments of the invention, will beapparent to those skilled in the art on reference to this description.It is therefore contemplated that the appended claims will cover anysuch modifications or embodiments as fall within the true scope of theinvention.

1. A semiconductor device comprising: a substrate; a first insulatorlayer formed on the substrate; a first conductive layer formed on thefirst insulator layer; a second insulator layer formed on the firstconductive layer, the second insulator layer including a through holehaving a substantially vertical side face; a second conductive layerformed on the second insulator layer; a sidewall structure formed on theside face of the through hole so that the sidewall structure graduallynarrows the through hole; and a fuse formed of a conductive materialthat buries the narrowed through hole, said fuse having a lower endconnected to the first conductive layer and an upper end connected tothe second conductive layer.
 2. A semiconductor device according toclaim 1, wherein the fuse and the second conductive layer are formed ofa same material.
 3. A semiconductor device according to claim 1, whereinthe sidewall structure includes a first layer formed on the side face ofthe through hole and a second layer formed on the first layer.
 4. Asemiconductor device according to claim 1, wherein a thickness of thesidewall structure is smallest at the substrate and becomes graduallylarger away from the substrate.
 5. A semiconductor device according toclaim 1, wherein the first and second conductive layers areinterconnections.
 6. A semiconductor device according to claim 1,wherein the first and second conductive layers are made of aluminum. 7.A semiconductor device according to claim 1, wherein the first andsecond insulator layers are made of silicon oxide.
 8. A semiconductordevice according to claim 3, wherein the first layer is formed ofsilicon nitride and the second layer is formed of silicon oxide.
 9. Asemiconductor device comprising: a semiconductor substrate; a firstdielectric film formed on the semiconductor substrate; a firstconductive film formed on the first dielectric film; a second dielectricfilm formed on the first conductive film, the second dielectric filmincluding a through hole that exposes the first conductive film; asidewall structure formed on a side surface of the through hole so thatthe sidewall structure gradually narrows the through hole; a conductivematerial filled in the narrowed through hole; and a second conductivefilm on the second dielectric film and the conductive material, so thatthe conductive material electrically connects the first and secondconductive films to each other.
 10. A semiconductor device according toclaim 9, wherein the conductive material and the second conductive filmare formed of a same material.
 11. A semiconductor device according toclaim 9, wherein the sidewall structure includes a first sidewall filmformed on the side surface of the through hole and a second sidewallfilm formed on the first sidewall film.
 12. A semiconductor deviceaccording to claim 9, wherein a thickness of the sidewall structure issmallest at the semiconductor substrate and becomes gradually largeraway from the semiconductor substrate.
 13. A semiconductor deviceaccording to claim 9, wherein the first and second conductive films aremade of aluminum.
 14. A semiconductor device according to claim 9,wherein the first and second dielectric films are made of silicon oxide.15. A semiconductor device according to claim 11, wherein the firstsidewall film is formed of silicon nitride and the second sidewall filmis formed of silicon oxide.
 16. A semiconductor device comprising: asemiconductor substrate; a first conductive film formed on thesemiconductor substrate; a dielectric film formed on the firstconductive film and the semiconductor substrate, the dielectric filmhaving a through hole that exposes the first conductive film; a sidewallstructure formed in the through hole so that the through hole isgradually narrowed by the sidewall structure to expose the firstconductive film; a fuse structure formed by a conductive material filledin the narrowed through hole; and a second conductive film on thedielectric film and the fuse structure, so that the fuse structureelectrically connects the first and second conductive films to eachother.
 17. A semiconductor device according to claim 16, wherein thesecond conductive film is formed of the conductive material.
 18. Asemiconductor device according to claim 16, wherein the sidewallstructure includes a first sidewall film formed on a side surface of thethrough hole and a second sidewall film formed on the first sidewallfilm.
 19. A semiconductor device according to claim 16, wherein thefirst and second conductive films are made of aluminum.
 20. Asemiconductor device according to claim 16, wherein the dielectric filmis made of silicon oxide.